1. Field of the Invention
The invention relates to an ink jet recording method and an ink jet recording device that are favorably used for formation of a high-quality image at high speed.
2. Description of the Related Art
An ink jet method of ejecting ink in the form of liquid droplets from an ink ejector has been used in various kinds of printers for the reasons of being compact and less expensive, capable of forming an image without contacting a recording medium, and the like. Among these ink jet methods, there are a piezo ink jet method utilizing deformation of piezoelectric elements to eject ink and a thermal ink jet method utilizing a boiling phenomenon of ink due to thermal energy to eject the ink in the form of droplets, which have the characteristics of high resolution and high-speed printability.
Improvements in speed and image quality have currently become important objectives, upon printing by ejecting ink droplets onto a plain paper sheet or a non-water absorbing recording medium made of plastics or the like with an ink jet printer.
Ink jet recording is a method of ejecting ink droplets according to image data to form a line or an image on a recording medium with the liquid droplets. However, there have been problems in practical use, particularly in a case of recording on the above-described non-absorbing recording medium, e.g., bleeding of an image easily occurs, or mixing of adjacent ink droplets occurs on the recording medium to inhibit formation of a sharp image, when it takes time for the liquid droplets to dry or penetrate into the recording medium after having been ejected. When the liquid droplets mix with each other, the ejected adjacent liquid droplets coalesce with each other to shift from the positions at which they have landed, thereby causing unevenness in line width in a case of forming fine lines or unevenness in color in a case of forming a colored area, or the like. Further, since the degree of occurrence of unevenness in line width or color unevenness in a colored area varies depending on ink absorption and wettability of the surface of the recording medium, there has also been a problem in that different images are formed on different types of recording media, even when the same ink is used under the same ejection conditions.
As a method of suppressing image bleeding or nonuniformity of line width, there is a method of promoting fixation of liquid droplets. For example, there have been disclosed methods of using inks of two-liquid type having reactivity and allowing them to react with each other on a recording medium to achieve a depicting property with high definition, such as a method of recording with ink containing an anionic dye after application of a liquid containing a basic polymer (for example, refer to Japanese Patent Application Laid-Open (JP-A) No. 63-60783), or a method of applying ink containing an anionic compound and a coloring material after application of a liquid composition containing a cationic substance (for example, refer to JP-A No. 8-174997).
An ink jet recording method has also been proposed in which an ultraviolet-curable ink is used as the ink, the ink dots ejected onto a recording medium are irradiated with ultraviolet rays in conformity with the timing of ejection, then the dots are pre-cured to be thickened to such an extent that the adjacent dots do not mix with each other, and thereafter the dots are further irradiated with ultraviolet rays to be completely cured (for example, refer to JP-A No. 2004-42548).
Further, a method has been proposed that improves visibility or bleeding of color ink or a problem such as variation in the obtained images formed on different types of recording media, by applying a radiation curable white ink to form a uniform undercoating layer on a transparent or semi-transparent non-absorbing recording medium, then curing or thickening the layer by irradiating with radiation rays, and thereafter recording with a radiation curable color ink (for example, refer to JP-A No. 2003-145745 and JP-A No. 2004-42525). There has also been proposed a method in which a substantially transparent actinic ray-curable ink is applied onto a recording medium in place of the above radiation curable white ink by an ink jet head (for example, refer to JP-A No. 2005-96254).
There have also been disclosed ink jet recording methods of curing type such as a method in which printing is performed by ejecting two types of solutions and irradiating with ultraviolet rays to form print dots (for example, refer to Japanese Patent No. 3478495) and others (for example, refer to JP-A Nos. 8-218018 and 2001-348519, Japanese Patent No. 3642152, JP-A Nos. 2000-135781 and 2003-12971).
However, in the method described in JP-A No. 2004-42548, although bleeding can be suppressed, there still remains a problem of variation in images among various types of recording media, and thus problems of unevenness in line width, color or the like due to mixing of ink droplets has not been sufficiently solved. These problems of unevenness in line width, color or the like due to mixing of ink droplets have also not been sufficiently solved by any of the methods described in JP-A Nos. 2003-145745 or 2004-42525. Further, there still remains a problem of unevenness in line width, color or the like due to mixing of ink droplets in the method described in JP-A No. 2005-96254.
Further, it is difficult to maintain the same shape and size of the dots forming an ejected area at the border between the ejected region in which an ink has been ejected and the non-ejected region. Therefore, there is a problem that the ejected ink flows toward the area around the border with less amount of the ink, thereby causing change in density along the border. In such a case, the image has an appearance as if it is outlined with a frame.
The invention has been made in view of the above problems and is intended to provide an ink jet recording method and an ink jet recording device by which images having excellent uniformity can be recorded on various types of recording media, ink bleeding or unevenness in line width or color due to coalescence between droplets can be suppressed (i.e., having dot reproducibility), and at the same time, the dot shape at the border of ejected region and non-ejected region can be maintained, thereby recording an image well reproduced to details irrespective of the form of the image.
The invention has been achieved based on the findings that when ink is simply ejected onto a liquid, a leveling effect of the liquid at the border of the ejected region and non-ejected region tends to occur, due to which a change in dot shape of the ejected ink is easily caused; and that the change in dot shape plays an important role in maintaining the density reproduction to details, over the whole image.